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XML, DTD, XML Schema

XML, DTD, XML Schema. Jianguo Lu University of Windsor. XML Basics. XML DTD XML Schema XSLT. Markup. What is XML (eXtremely Marketed Language). From XML Handbook. XML (eXtensible Markup Language). Markup in XML

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XML, DTD, XML Schema

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  1. XML, DTD, XML Schema Jianguo Lu University of Windsor 03-60-569

  2. XML Basics • XML • DTD • XML Schema • XSLT 03-60-569

  3. Markup What is XML (eXtremely Marketed Language) From XML Handbook 03-60-569

  4. XML (eXtensible Markup Language) • Markup in XML • A sequence of characters inserted into a text file, to indicate how the file should be displayed, or to describe the logical structure. • Markup is everything in a document that is not content. • Initially used in typesetting a document • Markup indicators are called tags. e.g. <font color=“blue”> • A pair of tags and the things enclosed in tags is called element. e.g. <font color=“blue”> formatted as blue </font> 03-60-569

  5. What is XML (eXtensible Markup Language) (cont.) • Extensible • In general: Something that is designed that users or later designers can extend its capability. • In XML: Allow you to define your own tags to describe data • You can represent any information (define new tags) • You can represent in the way you want (define new structure) • XML is a meta-language • A language to define other languages • Use DTD to define the syntax of a language 03-60-569

  6. Markup (and extensible) languages are not new • SGML (Standard Generalized Markup Language) • Markup, extensible • 1980: first publication, 1986: ISO standard • HTML(HyperText Markup Language) • Markup, hypertext, Subset of SGML • Started 1990, CERN (Centre Européen de Recherche Nucléaire, or European High-Energy Particle Physics lab) • Invented by Tim Berners-Lee • XML (eXtensible Markup Language) • Subset of SGML • Started 1996, adopted by W3C 1998 • Eliminate the complexity of SGML • Separate the data from the formatting information in HTML … … SGML HTML 03-60-569

  7. HTML • table: <table> • Table head: <TH> • Table row: <TR> • Table data: <TD> open tag, element name <html><body> Stock table <TABLE border="1"> <TR><TH> Exchange </TH> <TH> Name </TH> <TH> Price </TH> </TR> <TR><TD>nasdaq </TD> <TD>amazon corp </TD> <TD> 16.875 </TD> </TR> <TR><TD>nyse </TD> <TD> IBM inc </TD> <TD> 102.250</TD> </TR> </TABLE> </body></html> Attribute value attribute stock.html closing tag data Displayed in browser 03-60-569

  8. XML and HTML • Similarities: • They are both markup languages; • They are both simple. • Differences: 03-60-569

  9. element XML Example attribute <?xml version="1.0" ?> <stocks> <stock exchange="nasdaq"> <name>amazon corp</name> <symbol>amzn</symbol> <price>16</price> </stock> <stock exchange="nyse"> <name>IBM inc</name> <price>102</price> </stock> </stocks> element stock.xml • An XML document has a group of elements; • Each element has an opening tag and a closing tag; • An element can have attributes. 03-60-569

  10. Benefits of using XML <html><body> Stock table <TABLE border="1"> <TR><TH> Exchange </TH> <TH> Name </TH> <TH> Price </TH> </TR> <TR><TD>nasdaq </TD> <TD>amazon corp </TD> <TD> 16.875 </TD> </TR> <TR><TD>nyse </TD> <TD> IBM inc </TD> <TD> 102.250</TD> </TR> </TABLE> </body></html> <?xml version="1.0" ?> <stocks> <stock exchange="nasdaq"> <name>amazon corp</name> <symbol>amzn</symbol> <price>16</price> </stock> <stock exchange="nyse"> <name>IBM inc</name> <price>102</price> </stock> </stocks> 03-60-569

  11. Tree structure of XML <stocks> <stock exchange=“nasdaq”> <stock Exchange=“nyse” > <name> <price> <name> <price> <symbol> amzn 15.45 IBM 105 Amazon inc 03-60-569

  12. XML Element • An element consists of: • an opening tag • the content • a closing tag • Example: • <lecturer>David Billington</lecturer> • Tag names can be chosen almost freely. • The first character must be a letter, an underscore, or a colon • No name may begin with the string “xml” in any combination of cases • E.g. “Xml”, “xML” 03-60-569

  13. Contents of XML Elements • Content may be text, or other elements, or nothing <lecturer> <name>David Billington</name> <phone> +61 − 7 − 3875 507 </phone> </lecturer> <lecturer></lecturer> • If there is no content, then the element is called empty; it is abbreviated as follows: <lecturer/> 03-60-569

  14. Attributes • An attribute is a name-value pair inside the opening tag of an element <lecturer name="David Billington" phone="+61 − 7 − 3875 507"/> • Example <order orderNo="23456" customer="John Smith" date="October 15, 2002"> <item itemNo="a528" quantity="1"/> <item itemNo="c817" quantity="3"/> </order> 03-60-569

  15. Element and Attribute <order orderNo="23456" customer="John Smith" date="October 15, 2002"> <item itemNo="a528“ quantity="1"/> <item itemNo="c817“ quantity="3"/> </order> <order> <orderNo>23456</orderNo> <customer>John Smith</customer> <date>October 15, 2002</date> <item> <itemNo>a528</itemNo> <quantity>1</quantity> </item> <item> <itemNo>c817</itemNo> <quantity>3</quantity> </item> </order> • Attributes can be replaced by elements; • When to use elements and when attributes is a matter of taste; • But attributes cannot be nested. • Attributes can only have simple types. 03-60-569

  16. Further Components of XML Docs • Comments • A piece of text that is to be ignored by parser • <!-- This is a comment --> • Processing Instructions (PIs) • Define procedural attachments • <?xml-stylesheet type="text/xsl" href="stock.xsl"?> • This instruction tells the program, say, the browser, to use stocl.xsl to process the xml document. • We will see this processing instruction later in XSLT. • <?stylesheet type="text/css" href="mystyle.css"?> 03-60-569

  17. Well formed XML Document • An XML document is well formed if it conforms to XML syntax rules. • Additional rules: • XML document must have a root element • Attribute values must be quoted • XML is case sensitive • Try to find bugs in the following XML document: <?xml version="1.0" ?> <stock exchange="nasdaq"> <name>amazon corp </name> <symbol>amzn</symbol> <price>16</price> </stock> <stock exchange= nyse > <name>IBM inc</name> <price> 102 </PRICE> </stock> <stocks> </stocks> 03-60-569

  18. Valid XML document <?xml version="1.0" ?> <stocks> <name> <stock> 102</stock> </name> <price>IBM inc</price> <symbol>amzn </symbol> <price>16</price> <stock exchange="nyse"> <price> amazon </price> </stock> </stocks> • Problem: • Not every well formed document makes sense • Solution: • Associate XML with its “type”. • Valid XML document: conforms to its XML schema. 03-60-569

  19. XML DTD (Document Type Definition) • What: DTD is a set of rules to define the syntax of a language. It is similar to context free grammar. • Why: Help XML generation and processing. • How: Write a sequence of element declarations and attribute declarations. • Element declaration <!ELEMENT tagName tagContent> • Attribute declaration <!ATTLIST tagName [attName attContent]> Repeat 0 or more times Occur 0 or once. <!ELEMENT stocks (stock*)> <!ELEMENT stock (name, symbol?, price)> <!ATTLIST stock exchange CDATA > <!ELEMENT name (#PCDATA)> <!ELEMENT symbol (#PCDATA)> <!ELEMENT price (#PCDATA)> stock.dtd 03-60-569

  20. Another DTD example <order orderNo="23456“ customer="John Smith“ date="October 15, 2002"> <item itemNo="a528" quantity="1"/> <item itemNo="c817" quantity="3"/> </order> <!ELEMENT order (item+)> <!ATTLIST order orderNo ID #REQUIRED customer CDATA #REQUIRED date CDATA #REQUIRED> <!ELEMENT item EMPTY> <!ATTLIST item itemNo ID #REQUIRED quantity CDATA #REQUIRED comments CDATA #IMPLIED> • ID attribute values must be unique • IDREF attribute values must match some ID 03-60-569

  21. Element Declaration • General form: • <!ELEMENT tagName tagContent> • Example: • <!ELEMENT stock (name, symbol?, price)> • Content Model • Sequence, Choice, Cardinality • We express that a lecturer element contains either a name element or a phone element as follows: <!ELEMENT lecturer (name | phone)> • A lecturer element contains a name element and a phone element in any order. <!ELEMENT lecturer((name,phone)|(phone,name))> • Cardinality operators • ?: appears zero times or once • *: appears zero or more times • +: appears one or more times • No cardinality operator means exactly once 03-60-569

  22. Attribute declaration • General form: <!ATTLIST tagName [attName attContent]> • Example: • <!ATTLIST stock exchange CDATA > • <!ATTLIST item itemNo ID #REQUIRED quantity CDATA #REQUIRED comments CDATA #IMPLIED> • AttContent contains Attribute types and default values. 03-60-569

  23. Attribute types • Similar to predefined data types, but limited selection • The most important types are • CDATA, a string (sequence of characters) • Example: <!ATTLIST stock exchange CDATA > • ID, a name that is unique across the entire XML document • IDREF, a reference to another element with an ID attribute carrying the same value as the IDREF attribute • IDREFS, a series of IDREFs • (v1| . . . |vn), an enumeration of all possible values • Limitations: no data types for dates, integer, number ranges etc. • XML Schema will solve this problem 03-60-569

  24. Reference with IDREF and IDREFS XML Example <family> <person id="bob" mother="mary" father="peter"> <name>Bob Marley</name> </person> <person id="bridget" mother="mary"> <name>Bridget Jones</name> </person> <person id="mary" children="bob bridget"> <name>Mary Poppins</name> </person> <person id="peter" children="bob"> <name>Peter Marley</name> </person> </family> DTD: <!ELEMENT family (person*)> <!ELEMENT person (name)> <!ELEMENT name (#PCDATA)> <!ATTLIST person id ID #REQUIRED mother IDREF #IMPLIED father IDREF #IMPLIED children IDREFS #IMPLIED> What’s the corresponding concepts in database ? 03-60-569

  25. Enumerated attribute values • Syntax: <!ATTLIST element-name attribute-name (en1|en2|..) default-value> • DTD example: <!ATTLIST payment method (check|cash) "cash"> • Valid XML example: <payment method="check" /> or <payment method="cash" /> 03-60-569

  26. Attribute defaults • #REQUIRED • Attribute must appear in every occurrence of the element type in the XML document • #IMPLIED • The appearance of the attribute is optional • #FIXED "value" • Every element must have this attribute value • "value" • This specifies the default value for the attribute 03-60-569

  27. #FIXED value • Syntax <!ATTLIST element-name attribute-name attribute-type #FIXED "value"> • DTD example: <!ATTLIST sender company CDATA #FIXED "Microsoft"> • A valid XML: <sender company="Microsoft" /> • An invalid XML: <sender company=“IBM" /> 03-60-569

  28. Default value • Example DTD: • <!ELEMENT square EMPTY> • <!ATTLIST square width CDATA "0"> • Valid XML: • <square width="100" /> • <square/> 03-60-569

  29. DTD example for email • A head element contains (in that order): • a from element • at least one to element • zero or more cc elements • a subject element • In from, to, and cc elements • the name attribute is not required • the address attribute is always required • A body element contains • a text element • possibly followed by a number of attachment elements • The encoding attribute of an attachment element must have either the value “mime” or “binhex” • “mime” is the default value 03-60-569

  30. Email DTD <!ELEMENT email (head, body)> <!ELEMENT head (from, to+, cc*, subject)> <!ELEMENT from EMPTY> <!ATTLIST from name CDATA #IMPLIED address CDATA #REQUIRED> <!ELEMENT to EMPTY> <!ATTLIST to name CDATA #IMPLIED address CDATA #REQUIRED> <!ELEMENT cc EMPTY> <!ATTLIST cc name CDATA #IMPLIED address CDATA #REQUIRED> <!ELEMENT subject (#PCDATA)> <!ELEMENT body (text, attachment*)> <!ELEMENT text (#PCDATA)> <!ELEMENT attachment EMPTY> <!ATTLIST attachment encoding (mime|binhex) "mime" file CDATA #REQUIRED> 03-60-569

  31. Remarks on DTD • A DTD can be interpreted as an Extended Backus-Naur Form (EBNF) • <!ELEMENT email (head, body)> • is equivalent to email ::= head body • Recursive definitions possible in DTDs • <!ELEMENT bintree ((bintree root bintree) | emptytree)> 03-60-569

  32. Where we are • XML • DTD • XML Schema 03-60-569

  33. XML Schema—compared with DTD • Significantly richer language for defining the structure of XML documents • Its syntax is based on XML itself • not necessary to write separate tools • Reuse and refinement of schemas • Expand or delete already existent schemas • Sophisticated set of data types, compared to DTDs • Define new data types. • Built in data types: DTD supports 10; XML Schemas supports 44+ datatypes. 03-60-569

  34. From DTD to XML Schema <!ELEMENT BookStore (Book+)> <!ELEMENT Book (Title, Author, Date, ISBN, Publisher)> <!ELEMENT Title (#PCDATA)> <!ELEMENT Author (#PCDATA)> <!ELEMENT Date (#PCDATA)> <!ELEMENT ISBN (#PCDATA)> <!ELEMENT Publisher (#PCDATA)> 03-60-569

  35. <?xml version="1.0"?> <xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema" targetNamespace="http://www.books.org" xmlns="http://www.books.org" elementFormDefault="qualified"> <xsd:element name="BookStore"> <xsd:complexType> <xsd:sequence> <xsd:element ref="Book" minOccurs="1" maxOccurs="unbounded"/> </xsd:sequence> </xsd:complexType> </xsd:element> <xsd:element name="Book"> <xsd:complexType> <xsd:sequence> <xsd:element ref="Title" minOccurs="1" maxOccurs="1"/> <xsd:element ref="Author" minOccurs="1" maxOccurs="1"/> <xsd:element ref="Date" minOccurs="1" maxOccurs="1"/> <xsd:element ref="ISBN" minOccurs="1" maxOccurs="1"/> <xsd:element ref="Publisher" minOccurs="1" maxOccurs="1"/> </xsd:sequence> </xsd:complexType> </xsd:element> <xsd:element name="Title" type="xsd:string"/> <xsd:element name="Author" type="xsd:string"/> <xsd:element name="Date" type="xsd:string"/> <xsd:element name="ISBN" type="xsd:string"/> <xsd:element name="Publisher" type="xsd:string"/> </xsd:schema> <!ELEMENT BookStore (Book+)> <!ELEMENT Book (Title, Author, Date, ISBN, Publisher)> <!ELEMENT Title (#PCDATA)> <!ELEMENT Author (#PCDATA)> <!ELEMENT Date (#PCDATA)> <!ELEMENT ISBN (#PCDATA)> <!ELEMENT Publisher (#PCDATA)> 03-60-569

  36. XML Schema syntax • An XML schema is an element with an opening tag like <schema xmlns=“http://www.w3.org/2000/10/XMLSchema” version="1.0"> • Structure of schema elements • Element and attribute typesusing data types 03-60-569

  37. Element Types • Example <element name="email"/> <element name="head" minOccurs="1" maxOccurs="1"/> <element name="to" minOccurs="1"/> • Cardinality constraints: • minOccurs="x" (default value 1) • maxOccurs="x" (default value 1) • Generalizations of *, ?, + offered by DTDs <xsd:element name=“email" minOccurs="1" maxOccurs="1"/> Equivalent! <xsd:element name=“email"/> 03-60-569

  38. Attribute declaration • A simple attribute declaration example • Attribute definition: <xs:attribute name="lang" type="xs:string"/> • XML example with the attribute: <lastname lang="EN">Smith</lastname> • Data types • Declare default/optional/required/fixed values <attribute name="lang" type="xs:string" use="optional"/> <attribute name="lang" type="xs:string" use="required"/> • Note that we don’t need to specify the element name as in DTD. 03-60-569

  39. Data types • Built-in data types • Numerical data types: integer, Short etc. • String types: string, ID, IDREF, CDATA etc. • Date and time data types: time, Month etc. • User-defined data types • simple data types, which cannot use elements or attributes • complex data types, which can use these • Complex data types • sequence, a sequence of existing data type elements (order is important) • all, a collection of elements that must appear (order is not important) • choice, a collection of elements, of which one will be chosen 03-60-569

  40. Complex data type <complexType name="lecturerType"> <sequence> <element name="firstname" type="string" minOccurs="0“ maxOccurs="unbounded"/> <element name="lastname" type="string"/> </sequence> <attribute name="title" type="string" use="optional"/> </complexType> 03-60-569

  41. Data Type Extension • Data types can be extended by new elements or attributes. Example: <complexType name="extendedLecturerType"> <extension base="lecturerType"> <sequence> <element name="email“ type="string“ minOccurs="0" maxOccurs="1"/> </sequence> <attribute name="rank" type="string" use="required"/> </extension> </complexType> 03-60-569

  42. Resulting XML Schema <complexType name="extendedLecturerType"> <sequence> <element name="firstname" type="string" minOccurs="0" maxOccurs="unbounded"/> <element name="lastname" type="string"/> <element name="email" type="string" minOccurs="0" maxOccurs="1"/> </sequence> <attribute name="title" type="string“ use="optional"/> <attribute name="rank" type="string" use="required"/> </complexType> 03-60-569

  43. Data type restriction • An existing data type may be restricted by adding constraints on certain values • Restriction is not the opposite from extension • Restriction is not achieved by deleting elements or attributes • The following hierarchical relationship holds: • Instances of the restricted type are also instances of the original type; • They satisfy at least the constraints of the original type. 03-60-569

  44. Example of Data Type Restriction <complexType name="restrictedLecturerType"> <restriction base="lecturerType"> <sequence> <element name="firstname" type="string" minOccurs="1" maxOccurs="2"/> </sequence> <attribute name="title" type="string" use="required"/> </restriction> </complexType> <complexType name="lecturerType"> <sequence> <element name="firstname" type="string" minOccurs="0“ maxOccurs="unbounded"/> <element name="lastname" type="string"/> </sequence> <attribute name="title" type="string" use="optional"/> </complexType> 03-60-569

  45. Restriction of simple data types <simpleType name="dayOfMonth"> <restriction base="integer"> <minInclusive value="1"/> <maxInclusive value="31"/> </restriction> </simpleType> <simpleType name="dayOfWeek"> <restriction base="string"> <enumeration value="Mon"/> <enumeration value="Tue"/> <enumeration value="Wed"/> <enumeration value="Thu"/> <enumeration value="Fri"/> <enumeration value="Sat"/> <enumeration value="Sun"/> </restriction> </simpleType> 03-60-569

  46. Regular expression can be used <xsd:simpleType name="TelephoneNumber"> <xsd:restriction base="xsd:string"> <xsd:length value="8"/> <xsd:pattern value="\d{3}-\d{4}"/> </xsd:restriction> </xsd:simpleType> 03-60-569

  47. The email example revisited <element name="email" type="emailType"/> <complexType name="emailType"> <sequence> <element name="head" type="headType"/> <element name="body" type="bodyType"/> </sequence> </complexType> <complexType name="headType"> <sequence> <element name="from" type="nameAddress"/> <element name="to" type="nameAddress" minOccurs="1" maxOccurs="unbounded"/> <element name="cc“type="nameAddress" minOccurs="0" maxOccurs="unbounded"/> <element name="subject“type="string"/> </sequence> </complexType> 03-60-569

  48. Different ways to declare elements 1 <xsd:element name="name" type="type" minOccurs="int" maxOccurs="int"/> <xsd:element name="name" minOccurs="int" maxOccurs="int"> <xsd:complexType> … </xsd:complexType> </xsd:element> 2 <xsd:element name="name" minOccurs="int" maxOccurs="int"> <xsd:simpleType> <xsd:restriction base="type"> … </xsd:restriction> </xsd:simpleType> </xsd:element> 3 03-60-569

  49. Another way to define email schema <element name="email"> <complexType> <sequence> <element name="head" type="headType"/> <element name="body" type="bodyType"/> </sequence> </complexType> </element> <complexType name="headType"> <sequence> <element name="from" type="nameAddress"/> <element name="to" type="nameAddress" minOccurs="1" maxOccurs="unbounded"/> <element name="cc“type="nameAddress" minOccurs="0" maxOccurs="unbounded"/> <element name="subject“type="string"/> </sequence> </complexType> 03-60-569

  50. Using XML Schema/DTD • Data model • With XML Schemas you specify how your XML data will be organized, and the datatypes of your data. That is, with XML Schemas you model how your data is to be represented in an instance document. • A contract • Organizations agree to structure their XML documents in conformance with an XML Schema. Thus, the XML Schema acts as a contract between the organizations. • A rich source of metadata • An XML Schema document contains lots of data about the data in the XML instance documents, such as the datatype of the data, the data's range of values, how the data is related to another piece of data (parent/child, sibling relationship), i.e., XML Schemas contain metadata 03-60-569

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